Processes for preparing 2-CdA are known. European Patent Application No. 173,059 A2 and R. Robins et al., J. Am. Chem. Soc., 106, 6379 (1984) disclose the preparation of 2-CdA. The preparation consists of the glycosylation of 2,6-dichloropurine with 1-chloro-2'-deoxy-3',5'-di-O-p-toluoyl-b-D-erythro -pentofuranose to yield the N-9 glycosylated purine, 2,6-dichloro-9-(2-deoxy-3,5-di-O-p-toluoyl-b-D-erythropentofuranosyl)purin e, which i subsequently reacted with ammonia to yield 2-CdA. The synthesis of 2-CdA by this process, however, has several drawbacks. First, the 2,6-dichloropurine is a costly commercial intermediate. Second, the glycosylation of the 2,6-dichloropurine yields an N-7 glycosylated side product, 2,6-dichloro-7-(2-deoxy-3,5-di-O-p-toluoyl -.beta.-D-erythro-pentofuranosyl)purine, that has to be separated from the desired N-9 glycosylated product.
Processes are also disclosed for preparing compounds having the following formula ##STR5## wherein W.sup.1 is Cl or NH.sub.2, and W.sup.2 is Cl or NH.sub.2, from the natural nucleoside guanosine (See, M. Robins et al., Can. J. Chem., 59, 2601 (1981); M. Robins et at., Nuc. Acids Symp. Ser., 9, 61 (1981). M. Robins et al., Can. J. Chem., 59, 2601 (1981) also disclose a process for preparing a compound of the formula ##STR6## by reacting the aforesaid compound wherein W.sup.1 and W.sup.2 are Cl with ammonia in a protic solvent such as water or an alcohol. However, these publications do not disclose or suggest a method for effecting the 2-deoxygenation of these compounds.
In addition, processes are disclosed for effecting the 2'-deoxygenation of compounds of the following formula ##STR7## (See. M. Robins et al., J. Am., Chem. Soc., 103, 932 (1981); M. Robins et at., J. Am. Chem. Soc., 105, 4059 (1983)). These publications, however, do not disclose or suggest a process for converting a nucleoside having a halo substituent in the nucleotide moiety to their corresponding 2'-deoxygenated nucleosides. Furthermore, it is disclosed that the steps that are used to effect the deoxygenation are not applicable where the starting nucleoside has a halogenated nucleotide moiety, i.e., such a nucleoside cannot be converted to the corresponding 2-deoxygenated nucleoside due to the presence of the halo substituent. R. Robins et al., J. Am. Chem. Soc., 106, 6379 (1984); J. Montgomery, In "Nucleosides, Nucleotides, and their Biological Applications", J. Rideout, D. Henry, M. Beecham; Edgs.; Academic Press: New York, p.p. 19-46 (1983).
Consequently, none of the aforesaid publications disclose a process for preparing 2-CdA from a starting material other than 2,6-dichloropurine. In addition, the publications do not disclose a process for preparing 2-CdA that does not require a glycosylating reaction step or the separation of isomeric N-glycosylated products. Furthermore, there is no disclosure of the preparation of 2-CdA starting from a 2'-oxygenated nucleoside.